Piezo-electric pressure transducer



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G. VRIESEN PIEZO-ELECTRIC vPRESSURE TRANSDUCER Filed June 13, 1960 March 19, 1963 /f/vEA/Ton GERHARD RIESEN United States Patent O 3,082,334 PIEZO-ELECTRIC PRESSURE TRANSDUCER Gerhard Riesen, Winterthur, Switzerland, assignor to Schweizerische Lokomotivund Maschinenfabrik, Winterthur, Switzerland, a joint-stock company Filed June 13, 1960, Ser. No. 35,488 Claims priority, application Switzerland June 12, 1959 3 Claims. (Cl. S10-9.1)

The present invention relates to piezo-electric pressure transducers, particularly for measuring high frequency pressure oscillations and pressure shock waves, and in which the pressure responsive crystal is -contained in a closed casing.

The operation of piezo-electric pressure transducers may be subjected to disturbances caused by influences resulting from their xation in operating position. Fluctuations of clamping forces may be produced, -or example |by body sound, at the clamping point of the transducer casing, and in this case, such additional for-ces are partly transmitted to the internal members of the small instrument. In this case, the signals emitted by the pressure transducer contain both the components of the pressure normally acting upon the instrument and in addition also components resulting from the inuence of the stresses in the material occurring at the clamping point of the instrument. Accordingly, the indications obtained lby the transducer are distorted and incorrect.

It is an object of the invention to eliminate as much as possible the detrimental influence of the clamping yforces upon the indications of the instrument. According to the invention a holding sleeve carrying and enclosing the transducer casing is provided, said sleeve, however, being firmly connected to the casing of the pressure transducer only along a portion of its total length and destined to be clamped to the wall of the pressure space provided -for pressure measurements.

The present invention will now be described in more detail with reference to the accompanying drawings illustrating, by way of example, a preferred embodiment of the invention, and in which VFIGURE 1 is a fragmentary axial section through a pressure transducer of a type hitherto used, clamped to the wall of the space destined for pressure measurements; FIGURE 2 is an axial section through a pressure transducer according to the invention.

The pressure transducers illustrated in FIGURES 1 and 2 belong to the type of sleeve transducers 'in which the crystal column consisting of two quartz bars 1 and 2 is built into a steel sleeve 3 closed on the pressure side. The quartz bars are placed under initial stress by a steel cylinder 4 pressed into the sleeve 3. The annular diaphragm 6 is rolled into sealing contact with the housing and prevents pressure gases from penetrating into the annular gap 7 between sleeve 3 and housing 5.

When the quartz bars are stressed in longitudinal direction, a positive charge is developed on the outer surface of the quartz cylinder 1, 2, this charge being grounded by the steel sleeve 3 and the housing 5. A charge of opposite polarity is developed at the separating plane of the semi-cylindrical bars and picked up by a thin copper sheet 8 between the two bars, and passes through a conductor l9 to a metal contact member 10 in which the conductor 9 is clamped by a pin. This charge is then passed on by means of a connector plug assembly 11. The cavity 12 provided between the end of the insulator 23 and the steel cylinder 4 contains a drying agent which is adapted to absorb even minute traces of humidity which remained during the assembly of the instrument or which may have entered subsequently through tine crevices.

FIGURE 1 shows the arrangement hitherto employed ICC,

for clamping the pressure transducer to the wall 15 of the space destined for pressure measurements, and according to this arrangement the housing 5 comprises an enlarged portion 16 providing two shoulders 17 and 18. The housing is clamped to the wall 15 and tightened bctween the said shoulders by means of a nut 19. The presumable distribution of the lines of force produced by the clamping effect is indicated by a group of dotted curves 20. The indicated distribution is based on the assumption that in the zone of the enlarged portion of the housing 5 some of the lines of force, owing to the tight sea-t between housing 5 and steel sleeve 3, enter into the latter and even into the steel cylinder 4. This distribution of the lines of force causes small deformations in these members, which become effective in the quartz bars 1 and 2 as minute additional pressure actions and release corresponding signals in the instrument. Accordingly, when fluctuations of these clamping forces take place, caused for example by sound transmission, these fluctuations will also appear in the emission of signals from the crystals 1 and 2. The normal operation of the instrument is then disturbed and the indications recorded in the cathode ray oscillograph do not correspond to the actual pressure conditions prevailing in the pressure space.

As illustrated in FIGURE 2, in the arrangement according to the invention the housing 5 is not directly engaged by the clamping members, but is maintained by the intermediary of a separate holding sleeve 21 which surrounds and carries the housing 5. The sleeve 21 comprises three axially extending sections, a relatively thick and short section 21a located in the upper sleeve portion, a short top extension 2lb and a longer bottom sleeve extension 21e. The thicker section 21a of the holding sleeve 21 is firmly connected to the housing 5 of the pressure transducer by means of a pressure tit. The axial length of the section 21a is considerably shorter than the length of the corresponding enlarged portion 16 of the housing in FIGURE 1. For this reason, the lines of force 22 resulting from the clamping of the pressure transducer according to FIGURE 2 enter the housing only to a limited extent and `do not at all penetrate into the internal members of the instrument. The described disturbances of the -signal indications thus are substantially avoided. In this manner the pressure transducer is also better protected against shocks, since the action of the two thin extensions 2lb and 21C of the holding sleeve may be compared to that of very stii'r springs.

I claim:

1. In combination, a piezo-electric pressure transducer, particularly for measuring high frequency oscillations and pressure shock waves, said transducer having a housing, a closed chamber in said housing and a pressure responsive cry-stal in said chamber, said combination lfurther comprising a holding sleeve surrounding said transducer housing and having a rst portion tightly engaging said housing over a portion only of its axial length, and two further sleeve portions axially extending from opposite ends of said first -sleeve portion and having radial dimensions greater than said first sleeve portion, a lmounting Ifor said transducer having an aperture therethrough with a shoulder therearound, one of said further sleeve portions abutting said shoulder, and a clamping member engaged in said aperture and abutting the other of said further sleeve portions.

2. A pressure transducer according to claim 1, in which the further sleeve portion which is situated on the side of the yrst holding sleeve portion toward the pressure re- 0 ceiving end of said transducer is longer than the other further sleeve portion.

3. In combination, a piezo-electric pressure transducer,

aoaaaafr 3 particularly for measuring high `frequency oscillations and pressure shock waves, said transducer having a housing, a closed chamber in said housing and a pressure responsive crystal in said chamber, said `combination further comprising a holding sleeve surrounding said transducer 'housing and having a tirst portion tightly engaging said housing over a portion only of its axial length, and two further sleeve portions axially extending from opposite ends of said lrst sleeve portion, and having radi-al dimensions greater than said first sleeve portion, whereby when said transducer and sleeve are mounted in an aperture in 5 portions to hold the combination in place in the aperture.

References Cited in the fiile of this patent UNITED STATES PATENTS Grinstead July 2l, 1959 2,917,642 Wright et al Dec. l5, 1959 

1. IN COMBINATION, A PIEZO-ELECTRIC PRESSURE TRANSDUCER, PARTICULARLY FOR MEASURING HIGH FREQUENCY OSCILLATIONS AND PRESSURE SHOCK WAVES, SAID TRANSDUCER HAVING A HOUSING, A CLOSED CHAMBER IN SAID HOUSING AND A PRESSURE RESPONSIVE CRYSTAL IN SAID CHAMBER, SAID COMBINATION FURTHER COMPRISING A HOLDING SLEEVE SURROUNDING SAID TRANSDUCER HOUSING AND HAVING A FIRST PORTION TIGHTLY ENGAGING SAID HOUSING OVER A PORTION ONLY OF ITS AXIAL LENGTH, AND TWO FURTHER SLEEVE PORTIONS AXIALLY EXTENDING FROM OPPOSITE ENDS OF SAID FIRST SLEEVE PORTION AND HAVING RADIAL DIMENSIONS GREATER THAN SAID FIRST SLEEVE PORTION, A MOUNTING FOR SAID TRANSDUCER HAVING AN APERTURE THERETHROUGH WITH A SHOULDER THEREAROUND, ONE OF SAID FURTHER SLEEVE PORTIONS ABUTTING SAID SHOULDER, AND A CLAMPING MEMBER 